Sunlight reflected off the water and traveling upwards makes the reflection
bow. To raindrops, the reflected light appears to come from a second
sun the same angular distance below the water as the real sun is above
it.

The ‘second sun’ forms a rainbow centered on a point
opposite in the sky called the ‘anthelic point’. The reflection
bow intersects the ordinary primary at the horizon and curves above it
in the sky.

Secondary bows also produce reflection rainbows.

Bows in the water
The bows below the horizon are not reflections in the true sense. They
are formed by different raindrops from the ones that formed the sky bows.

Reflected bows are made by rays that are reflected by the water surface
after they have passed through raindrops. The reflection inverts
the rainbow and the bow centre is then above the horizon at the anthelic
point. The reflection bow and ordinary bow meet in a cusp at the
horizon.

The reflected - reflection bow below the horizon is formed by a tortuous
ray path. Sunlight reflects off the water and travels upwards. It then
meets raindrops which form rainbow rays. These reflect again off the water
into the eye.